1. Field of the Invention
The present invention relates to the field of programmable fuse circuits. More specifically, the present invention relates to a programmable fuse circuit which allows a packaged integrated circuit to be programmed without the need for an extra package pin to control the programming function.
2. Brief Description of the Prior Art
It is common in the manufacture of the integrated circuit memories to have a defect occur in one portion of the memory array. It is desirable to use the functional portion of these memories as partial memories having total memory sizes smaller than the size of the original memory. Specifically, 8K Rams having defects in one portion of their memory array can often be used as 4K RAMS. However, it is necessary to specify which pin or which side of the partially functional memory is defective so that only the functional side of the memory array is used. Typically it is necessary to specify that one of the address pins of the partially functional memory is to be held at a specific voltage level to select the functional portion of the memory array.
In another type of semiconductor circuit a metal mask option can be applied as the last step in the manufacture of a semiconductor memory to provide connections which selectively activate desired circuit functions. For example, by proper design of the memory circuitry and the interconnects formed by the metal mask options, the memory can be selectively configured in either a 1K by 4-bit format or a 4K by 1-bit format. However, it would be desirable to be able to make a single part which could be selectively programmed to the desired memory format without the need for alternative metal masks. This would eliminate the need for separate metal masks and the need to inventory either partially completed memory circuits or two different types of memory circuits.
Similarly, mask options are often used to code select addresses into comparators of memories with multiple chip-select inputs. However, this requires the sorting and separate storing of memories programmed with each of the possible chip addresses. Again, it is desirable to have a single memory circuit which can be programmed to have any of the desired chip select addresses.